1. Field of the Invention
The invention relates to plasticiser-containing films based on polyvinyl acetal with UV stabilisers that have a low tendency toward migration, and glass laminates produced therewith.
2. Background Art
Commercially available plasticiser-containing polyvinyl butyral film (PVB film) for laminated glazings has been provided with UV absorbers for many decades so that UV radiation cannot penetrate through the laminated glass completely, in contrast to visible light. Protection against harmful UV radiation for individuals or objects located behind the laminated glass can thus be ensured in a simple manner. Besides the protection against cuts, this constitutes the main property advantage compared with monolithic glass, since such glass is largely transparent to UV radiation.
Derivatives or dimers of 2 hydroxyphenylbenzotriazole have proven their worth and are used in a widespread manner as UV absorbers and are obtainable using different substitution patterns, for example under the trade names Tinuvin P, Tinuvin 328, Tinuvin 327, Tinuvin 326 and Tinuvin 360.
Furthermore, derivatives of 2-hydroxybenzophenone are suitable as UV absorbers and are obtainable using different substitution patterns, for example under the trade names Mark LA 51, Seesorb 1000, Uvinul 30340, Uvinul 400, Cyasorb UV-24, Uvinul 3008 and Chimasorb 125.
In addition, derivatives of 2-hydroxyphenyltriazine are suitable as UV absorbers and are obtainable using different substitution patterns, for example under the trade names Tinuvin 1577 and Cyasorb UV-1164.
Compounds of this type are sketched in the general Formulas 1a, 1b, 2 and 3 and are known in PVB film for their excellent long-term stability, good solubility and high absorption capacity in almost the entire UV range. Furthermore, the specified UV absorbers can be introduced particularly easily into the film compound during the extrusion process since they are also relatively well soluble even in the plasticisers used conventionally, such as 3G8, and can thus be easily added to the plasticiser before extrusion. In addition, the above-mentioned UV absorbers have melting points that lie significantly below the extrusion temperature conventional with PVB film of approximately 200° C. These solubility and melting properties of the specified UV absorbers are promoted by the relatively low molecular weight thereof. This, together with the good solubility in the film matrix, also leads however to a high migration ability therein. Particularly in the field of architecture, laminated safety glass (LSG), once installed, is only replaced in some circumstances after a number of decades, such that permanent UV protection cannot be maintained with creeping loss of UV absorber via the open edges of the LSG.
The migration ability also not only has the disadvantage of reducing or completely eliminating the UV protective function associated with the UV absorber due to a loss of said absorber. The migration of the UV absorber is additionally disadvantageous when a film containing UV absorber is used in direct contact with a film free from UV absorber or a material free from UV absorber. In such an arrangement the UV absorber capable of migration may, over time, enter the layer initially free from UV absorber, may damage this layer as a result, or may trigger undesirable effects, such as clouding, disolouration or the loss of a certain functionality.
In order to reduce or completely prevent the migration of the UV absorber, insoluble UV absorbers with high molecular weight or high melting points, which lie above the usual extrusion temperature of approximately 200° C., can be used. These UV absorbers indeed have a lower tendency toward migration, but cause increased clouding in the film, which is produced by agglomeration of undissolved and non-uniformly distributed UV absorbers in the film matrix.